OBJECTIVES: 1) To determine by means of immunofluorescence the cellular source of testosterone and B17-estradiol synthesis in the gonads of the chick embryo as well as the day of incubation when these steroid hormones are first synthesized. 2) To determine by means of radioimmunoassay the day of incubation that testeosterone and B17-estradiol are first present in the blood of the chick embryo.. In both instances (1 & 2) the effect of hypophysectomy on the times of initial synthesis, as well as sustained production and secretion of these steroid hormones will be evaluated. The effect of pituitary transplants and gonadotrophin administration to hypophysectomized chick embryos will also be evaluated. BIBLIOGRAPHIC REFERENCES: Woods, J.E. and Podczaski, E.S. (1976). Functional Maturation of the Adenohypophysial-Testicular in the Chick Embryo. Amer. Zool. (Abstract). Woods, J.E. and Podczaski, E.S. (1976). Functional Maturation of the Adenohypophysial-Testicular Axis in the Chick Embryo.